It is known to use stepping motors, specifically microstepping motors, in robots for movement of extremities such as arms.
In normal situations such microstepping motors operate in an open loop system. In such systems an ordered position signal for a desired position of the motor, e.g. rate and direction signals, is received by a motor drive assembly. The drive assembly has a memory (logic circuit) and means to convert the position signal into discrete voltages to drive the motor. After the conversion of the position signal, the motor is driven in accordance with the applied voltage in discrete magnetic steps. However, the torsional load on the motor created by movement of the load causes an angular position error (or lag) in the motor. This will result in an improper final position for the load moved by the motor.
In robotic applications in which full stepping or microstepping motors are operated in an open loop, there are no means to compensate for the error caused by the torsional load on the motor. Because of this, the resultant error can be as much as + or - one magnetic step depending on the amount of the load.
When the motor encounters a load, it lags in position up to one magnetic step or less depending on the size of the load. If the motor is decelerating or braking, torque is being applied to the motor from the load a and phase lead of up to one magnetic step occurs. In either case, the motor's positional accuracy is degraded.
The present invention overcomes this problem by providing a torque loop control system and method to control the microstepping motor when it experiences a torsional load.